1. Field of the Invention
The present invention is directed to exhaust gas recirculation (EGR) systems. In particular, the present invention is directed to exhaust gas recirculation measurement devices for EGR systems that allow measurement of exhaust gas flow, even when the exhaust gas is flowing in a reverse direction.
2. Description of Related Art
The standards for vehicle emissions and other applications utilizing internal combustion engines have continued to increase to minimize environmental impact of fossil fuels. In particular, governmental regulations continue to require more and more fuel efficient vehicles and internal combustion engines with reduced emissions. Various emission components such as hydrocarbons (HC), nitrous oxides (NOx), particulates and other emission components have been significantly reduced recently by internal combustion engine manufacturers in view of these regulations, and the benefits to the environment. Many different methods have been utilized by manufacturers of internal combustion engines to reduce emissions including the use of catalytic converters, particulate traps, exhaust gas recirculation (herein after xe2x80x9cEGRxe2x80x9d) systems, as well as other devices and techniques.
EGR systems typically operate by diverting a portion of the exhaust gases emitted by the internal combustion engine back to the intake airflow of die engine. The recirculated exhaust gas mixes with the intake air and is used in the combustion of additional fuel. Such recirculation of at least a portion of exhaust gases generated by the internal combustion engines reduces emissions of the engines, and has been used in the automotive industry for many years. To ensure proper operation of the internal combustion engine, the amount of exhaust gas that is recirculated by the EGR system must be controlled based on the operating conditions and parameters of the engine. Thus, many EGR systems include a valve that regulates the amount of exhaust gas that is recirculated to the intake of the engine, the valve being controllable based on the operating conditions and parameters.
In the above regard, various EGR systems have been proposed in the art. For example, Japanese Patent 3-290051 to Makoto discloses an EGR system where a portion of the engine exhaust gas is introduced into a suction pipe and a single pitot tube is installed at the exhaust part of an EGR passage. U.S. Pat. No. 6,230,697 to Itoyama et al. discloses an EGR control system which includes an air flow rate detection means for detecting a flow rate of intake air drawn into an internal combustion engine to output an air flow rate indicative signal. However, Itoyama et al. does not disclose a particular device for accomplishing the desired air flow rate detection.
Moreover, whereas various other devices for measuring airflow are known in the art, such devices are not applied to EGR systems of internal combustion engines and have not been shown to be effective in such applications where the gas being measured is exhaust gases of internal combustion engines having emission components of combustion such as particulates.
For example, U.S. Pat. No. 4,478,075 to Oyama et al. discloses an air flow meter where a protective plate associated with the upstream inlet is provided on the upstream side of a by-pass passage to prevent dust from entering the by-pass passage. The flow meter includes a venturi structure connected to a passage that is connected with the main passage via rectangular bore. Oyama et al. also discloses that the ratio of a flow rate of the air flowing in the by-pass passage to that of the air flowing in the main passage is set in advance to a predetermined level. The Oyama et al. reference further discusses the issue of reverse flow in an engine air handling system as it relates to intake air, but does not discuss an EGR measurement device that is used for an EGR system.
U.S. Pat. No. 3,910,113 to Brown discloses a pipe insert having a pressure sensing form including high pressure and low pressure taps on the high pressure and low pressure sides of the form. The Brown reference further discusses the issue of reversed flow within the pipe. However, the Brown reference does not disclose or otherwise suggest use of the pipe insert with an EGR system. U.S. Pat. No. 4,463,601 to Rask discloses a mass airflow measurement apparatus which addresses the issue of reverse flow. The apparatus of Rask includes center body which divides the airflow of the engine into two concentric branches which have different flow splits in forward and reverse directions where the reverse flow in one of the branches is greater than in the forward flow. The Rask reference, however, does not disclose or suggest the use of the mass airflow measurement apparatus in an EGR system.
U.S. Pat. No. 5,088,332 to Merilainen et al. discloses a gas flow restricting and directing device that measures flow in medical respirators and also addresses the issue of reverse flow. The gas flow restricting and directing device of Merilainen et al. includes apertures around which vanes or baffles are provided. However, as noted, this reference relates to medical respirators and does not disclose or otherwise suggest use of the gas flow restricting and directing device that measures flow in an EGR system.
As evident from the discussion provided below, there exists an unfulfilled need for an EGR measurement device that will allow precise measurement of the exhaust gas recirculated. There also exists an unfulfilled need for such an EGR measurement device that will allow measurement of exhaust gas recirculated when the exhaust gas is flowing in the reverse direction. There further exists an unfulfilled need for such an EGR measurement device that is cost effective to manufacture.
In order for the EGR system to precisely regulate the amount of exhaust gas that is recirculated into the intake of the internal combustion engine, accurate measurement of the EGR flow is required. It has been found that EGR flow is highly pulsitile, i.e. occurs in pulses, due to the exhaust valve events. The portion of the exhaust gas being recirculated generally flows from the exhaust of the internal combustion engine to the intake of the internal combustion engine. However, there are short periods of time where the flow of the exhaust gas in the EGR system reverses in direction so that the exhaust gas being recirculated flows from the intake side to the exhaust side of the internal combustion engine as the pressure in the exhaust manifold bottoms out.
The current method of quantifying EGR flow is to measure the pressure differential across an EGR measurement device in the EGR system that produces a total-to-static pressure drop. The Bernoulli equation is then used with the measured pressure differential to calculate the flow rate of the exhaust gas being recirculated to the intake of the internal combustion engine. As noted above, because the flow direction actually reverses for short time periods, it has been found to be desirable to provide a measurement device that allows a total-to-static pressure to be produced regardless of the direction of EGR gas flow. The prior art devices described above which are applicable to EGR systems do not have this capability of measuring exhaust gas recirculation flow when the exhaust gas is flowing in a reverse direction, and do not even recognize this issue of reverse flow in EGR systems.
FIG. 1 shows graph 1 with the desired pressure response as line 2 which may be attained by implementing the measurement device using an orifice in both the forward flow direction and the reverse flow direction. As shown, the x-axis of the graph 1 indicates the mass flow in pound of mass per minute (lbm/min) while the y-axis of the graph 1 indicates the delta pressure, i.e. the pressure differential, in pounds per square inch (psid). As shown, for the same mass flow, the pressure differential (delta-P) is the same magnitude in the reverse direction as it is in the forward direction except the changes in sign. The disadvantage and problem with implementing the measurement device as an orifice is that the pressure losses are very high which detrimentally effects fuel economy and power density of the internal combustion engine.
The measurement device may alternatively be implemented using a conventional venturi. Venturis are generally provided with diffuser sections that recover static pressure, and thus, reduce flow losses as compared to orifices. The performance data of a conventional venturi is also shown in FIG. 1 as series of circle data points 3. By utilizing a conventional venturi as the measurement device, the total pressure losses are significantly reduced than when utilizing an orifice. As shown, in the forward flow direction, the performance of venturis closely corresponds to the performance of the orifice. However, as also shown in FIG. 1, venturis do not produce the correct pressure differential response when the flow reverses direction, i.e. when the portion of the exhaust gas to be recirculated flows from the intake of the internal combustion engine to the exhaust of the internal combustion engine.
In the above regard, FIG. 2A shows a conventional venturi 5 where the exhaust gas xe2x80x9cGxe2x80x9d is flowing in the forward direction to the intake of the internal combustion engine as indicated by arrow xe2x80x9cFxe2x80x9d. FIG. 2B shows the conventional venturi 5 where the exhaust gas xe2x80x9cGxe2x80x9d is flowing in the reverse direction as indicated by arrow xe2x80x9cRxe2x80x9d. The venturi 5 is provided with tap A positioned at the inlet section of the venturi 5, and tap B that is positioned at the throat section of the venturi 5. Tap A and tap B may be used to obtain pressure information pressure differential, i.e. the pressure difference between tap A and tap B, which may then be utilized to determine mass flow using the Bernoulli equation with some corrective parameters.
In the forward direction as shown in FIGS. 1 and 2A, a pressure differential is produced which closely approximates the true total-to-static pressure differential. Since the flow velocity is low at tap A, the upstream pressure at tap A approximates the total pressure and the downstream pressure at tap B approximates the static pressure. Correspondingly, the total-to-static pressure differential may be readily determined.
In the reverse direction as shown in FIGS. 1 and 2B, an incorrect response is produced. Because tap B does not sense the total pressure of the flow in the reverse direction, the total-to-static pressure differential is highly inaccurate. In addition, the exhaust gas flowing in the reverse direction through the conventional venturi 5 partially separates form the inlet wall resulting in a rectified pressure difference with a positive change in pressure differential (delta-P) being produced as shown by the circle data points 3 of FIG. 1. Clearly, this results in erroneous flow measurement and precise monitoring and control of the amount of exhaust gas being recirculated by the EGR system cannot be attained.
In view of the foregoing, an advantage of the present invention is in providing an EGR measurement device that will allow precise measurement of pressure of the exhaust gas recirculated by the EGR system to allow the flow rate to be determined.
Another advantage of the present invention is in providing such an EGR measurement device that will allow measurement of the exhaust gas recirculated, even when the exhaust gas is flowing in the reverse direction.
Still another advantage of the present invention is in providing such an EGR measurement device that may be manufactured economically.
These and other advantages are provided by an EGR measurement device for recirculating a portion of the exhaust gas of an internal combustion engine in accordance with the present invention. In one embodiment, the EGR measurement device includes an exhaust gas inlet section having a substantially cylindrical shape, a convergent cone section connected to the exhaust gas inlet section, and a diffuser section connected to the convergent cone section. The convergent cone section includes a cone inlet, a throat portion, and a cone outlet that is radially smaller than the cone inlet, while the diffuser section includes a diffuser inlet, a divergent conical portion, and a diffuser outlet that is radially larger than the diffuser inlet. In accordance with the present invention, a means is provided for accurately measuring exhaust gas flow in the EGR measurement device when the exhaust gas flows in a reverse direction that is opposite to the forward direction.
In accordance with one embodiment of the present invention, the EGR measurement device includes a first tap in fluidic communication with the exhaust gas inlet section to allow measurement of a first pressure indicative of pressure of the exhaust gas in the exhaust gas inlet section, and a second tap positioned downstream of the first tap to allow measurement of a second pressure indicative of pressure of the exhaust gas downstream of the first tap. Accurate measurement of exhaust gas flowing in the forward direction and the reverse direction may be attained based on a pressure difference between the first pressure and the second pressure.
In one preferred embodiment, the means for accurately measuring exhaust gas flow in the reverse direction includes an extension portion that extends substantially over the second tap, the extension portion defining an alcove that is fluidically open in the forward direction to the throat portion of the convergent cone section and/or the divergent conical portion of the diffuser section.
In another implementation, the exhaust gas inlet section and the convergent cone section are formed together as an integrated component that is secured to the diffuser section, the throat portion of the convergent cone section defining the extension portion substantially extending over the second tap to define an annular alcove that is fluidically open in the forward direction. The diffuser section may also include a substantially straight tubular portion upstream in the forward direction of the divergent conical portion.
In accordance with another implementation, the convergent cone section is formed as an insert, the throat portion of the convergent cone section defining the extension portion substantially extending over the second tap. In this regard, the throat portion may be provided with an indentation that defines the extension portion substantially extending over the second tap.
In still another embodiment, the EGR measurement device may be provided with a convergent cone section that is formed as an insert, the throat portion of the convergent cone section having a first indentation that defines the extension portion substantially extending over the first tap and forming a first alcove, and having a second indentation that defines a second extension portion that substantially extends over the second tap, the second extension portion defining a second alcove.
In accordance with another embodiment of the present invention, the EGR measurement device may include a first tap in fluidic communication with the exhaust gas inlet section to allow measurement of a first pressure indicative of pressure of the exhaust gas in the exhaust gas inlet section, and a pitot tube having an opening positioned at substantially center of the throat portion of the convergent cone section to allow measurement of a second pressure indicative of pressure of the exhaust gas in the throat portion of the convergent cone section. Preferably, the pitot tube is fluidically open in the forward direction.
In accordance with still another embodiment, the means comprises a first pitot tube positioned at substantially center of the throat portion of the convergent cone section, the first pitot tube having an opening fluidically open in the reverse direction to allow measurement of a first pressure, and a second pitot tube positioned at substantially center of the throat portion of the convergent cone section, the second pitot tube having an opening fluidically open in the forward direction to allow measurement of a second pressure.
In this regard, in one implementation, the first pitot tube and the second pitot tube may be secured to one another. In another implementation, the first pitot tube and the second pitot tube may be provided on a blade positioned at substantially center of the throat portion of the convergent cone section. The first pressure may be static pressure or total pressure, and the second pressure, the other pressure.
These and other advantages and features of the present invention will become more apparent from the following detailed description of the preferred embodiments of the present invention when viewed in conjunction with the accompanying drawings.